Three component insulating enamels for transformer wire are described in U.S. Pat. No. 4,215,174 and consist of a mixture of polyvinyl acetal, phenolaldehyde and epoxy resins. The patent discloses a three-component coating composition that reduces the amount of solvents when applied from a wet coating and improves the flow properties of the coating when applied by dry electrostatic techniques. The composition disclosed within the aforementioned U.S. patent is incorporated herein for purposes of reference.
U.S. patent application, Ser. No. 595,034, filed July 30, 1975, now abandoned and replaced by continuing application Ser. No. 697,838, filed June 21, 1976, now abandoned, in favor of appliction Ser. No. 103,080 filed Dec. 12, 1979 which issued as U.S. Pat. No. 4,277,534, describes the resin composition as well as the solvents employed in preparing the resins for application. Once the compositions are applied to transformer conductors, the solvent such as cresol, having a boiling point of approximately 200.degree. C. must be evaporated. Because of the high boiling point involved, recovery of the solvent in a closed system can be quite expensive.
In order to insure homogeneous mixing between the three resin components for electrostatic powder applications, the materials must be processed by one of several methods. One method is to dissolve the resins in a solvent and use a spray-dry process wherein the resin solution is propelled through a nozzle into a heated container. In a more commonly employed method the component resins are intimately mixed by hot melt or extrusion techniques followed by cryogenic grinding to produce a homogenous powder with the desired particle size distribution.
The processing methods for insuring intimate mixtures between the resin components of the wire coating composition make the prior art processes quite expensive in a large-scale transformer wire processing operation. The purpose of this invention is to provide methods and materials for processing wire coating compositions manufactured from several different resins by an economic process which allows for near total recovery of the solvent employed in the coating formation process.